Ecological safety requires that the long-lived radionuclides generated in spent nuclear fuel reprocessing be converted into the forms preventing their penetration into the environment during storage. Therefore it is necessary therewith to provide the recovery of uranium, plutonium and transplutonium elements (TPE), especially americium and curium.
Liquid extraction is the most widespread method for reprocessing of liquid high-level waste (HLW). Standard PUREX-process for TBP (tributylphosphate) extraction of uranium and plutonium from acidic solutions is known [Reactor Handbook, Sec. Edition, Ed. S. M. Stoller, R. B. Richards, v.2, Fuel reprocessing, p. 101 (1961) Interscience publ. Inc., NY]. In PUREX-process the extraction mixture of 1.1 M TBP in saturated hydrocarbons is used: it extracts uranium and plutonium well, but recovers all other elements very weakly.
It is also known TRUEX-process involving the recovery of americium and curium from acidic solutions, as well as rare-earth elements (REE) [E. P. Horwitz, et al, Solv. Extr. Ion Exch., v.3(1&2), p. 75, 1985]. In TRUEX-process the extraction mixture of 0.15-0.25M phenylotcyl-N,N-diisobutylcarbamoylphosphine oxide and 0.1-1.5M TBP in saturated hydrocarbons is used to recover trivalent elements and small quantities of uranium and plutonium from acidic solutions.
The extraction mixture used in the method for extraction of REE, TPE, U and Pu by diphenylcarbamoylphosphine oxide in fluorinated diluents is most similar to the extraction mixture applied in the patent draft [B. F. Myasoedov, M. K. Chmutova, V. A. Babain, A. Yu. Shadrin, V. P. Popik, G. A. Pribulova, E. G. Dzekun. Russian Certificate of Authorship No. 1524519 (converted to patent on Apr. 27, 1997), “Method for extraction recovery of rare-earth and actinide elements”]. This method is based on extraction mixture of 0.05-0.3M diphenyl-N,N-dibutylcarbamoylphosphine oxide solution in metanitrobenzotrifuoride or ortho-nitrophenyltetrafluoroethyl ether as prototype.
Drawback of the prototype is concerned with the fact that, in the presence of appreciable uranium quantities (U concentration more that 5 g/L(liter)) in aqueous phase, the precipitation solvate of uranium with carbamoylphosphine oxide is formed in organic phase; in this case the extraction process cannot be conducted under dynamic conditions.